This invention relates to a heat exchanger and a brazing method. The present invention is effective when applied to an oil cooler for cooling engine oil of cars and operating oil for automatic transmissions (ATF) (hereinafter merely called xe2x80x9coilxe2x80x9d), and to the brazing of the members.
Oil coolers of cars generally have a construction in which a heat exchange core (hereinafter called merely the xe2x80x9ccorexe2x80x9d) produced by stacking a plurality of plates in a direction of their thickness is assembled into a substantial cylindrical casing, and a seal surface plate is brazed to an open portion of the casing while closing the open portion lest the core falls from inside the casing.
Here, the seal surface plate plays a sealing function of sealing a gap between an engine and an oil cooler and preventing the engine oil from leaking, and also a function of a fitting bracket for fitting the oil cooler to the engine (cylinder block). Therefore, a contact surface (particularly, an O-ring groove) of the seal surface plate with the engine (cylinder block) is so finished, by machining it, to possess surface texture of not greater than 12.5 z.
The inventors of the present invention have attempted to reduce the weight of the oil cooler by using aluminum as a material of the plate (core), the casing and the seal surface plate, and have encountered the following problems.
When brazing is conducted under heating inside a furnace, oxygen in the atmosphere forms an oxide film on the surface of aluminum, thereby impeding brazing. To braze not only the oil cooler but also those articles which are made of aluminum, a method has been generally employed that applies a flux for removing the oxide film on the aluminum material (the plate, the casing and the seal surface plate in this example) clad with the brazing material, and conducts heat-brazing in an inert gas atmosphere such as nitrogen.
As described above, however, the oil cooler includes a large number of components that are fitted by brazing. If the flux is applied to each of these components, the number of production steps of the oil cooler drastically increases, thereby increasing the cost of production.
The flux so applied remains on the surface of each component even after brazing is complete, and this remaining flux (hereinafter called the xe2x80x9cflux residuexe2x80x9d) increases the surface texture. In consequence, the components for which predetermined surface texture is required, such as the seal surface plate, cannot secure predetermined surface texture after brazing is complete.
In view of the problems described above, the present invention aims at securing a predetermined surface texture on a seal surface plate even after completion of brazing while reducing the number of process steps necessary for applying a flux.
To accomplish this object, the present invention provides a heat exchanger comprising a casing having an opening for inserting a heat exchange core, for storing the heat exchange core, fall preventing members to prevent the heat exchange core falling from the casing, brazed to the casing after being fixed to the casing, and a seal surface plate finished to predetermined surface texture and brazed to at least one of the sides of the fall preventing members and the casing after the heat exchange core and the fall preventing members are fixed to the casing.
According to this construction, an assembly comprising the heat exchange core and the casing can be dipped into a flux before the seal surface plate is assembled. Consequently, a flux residue on the seal surface plate can be drastically reduced after brazing is complete.
As the assembly is dipped into the flux, the number of process steps necessary for applying the flux can be reduced, and predetermined surface texture can be secured on the seal surface plate even after brazing is complete.
A brazing method of a heat exchanger according to the present invention comprises a temporary assembly step of storing a heat exchange core in a casing, and fixing fall preventing members, to prevent the heat exchange core falling from the casing, to the casing, a dipping step of dipping an assembly of the heat exchange core, the casing and the fall preventing members into a flux after the temporary assembly step is complete, and a brazing step of integrally brazing the heat exchange core, the casing, the fall preventing members and a seal surface plate finished to predetermined texture under the state where the seal surface plate is brought into contact with at least one of the sides of the fall preventing members and the casing, after the dipping step is complete.
In consequence, the flux residue on the seal surface plate can be drastically reduced after brazing is complete, and predetermined surface texture can be secured on the seal surface plate even after completion of brazing while the number of process steps necessary for applying the flux is reduced.
The above and other features of the present invention will be more fully understood from the following description of preferred embodiments taken in connection with the accompanying drawings.